CETACEA. 587 



mediate organ (or labyrinth) and the tym- stretched, and another opening, which is the 



panum. communication with the sinuses. 



" The immediate organ is, in point of situa- *' The surface of the bone containing the im- 



tion to that of the tympanum, superior and in- mediate organ (the petrous bone, p, Jig. 269) 



ternal, as in the quadruped. The tympanum opposite to the mouth of the tympanum is very 



is open at the anterior end, where the Eusta- irregular, having a number of eminences and 



chian tube begins. cavities." 



" The Eustachian tube opens on the outside According to the Baron Cuvier* the petrous 



of the upper part of the fauces : in some higher bone in the Delphinid<e is permanently lodged 



in the nose than others ; highest, I believe, in between the temporal and contiguous parts of 



the Porpoise. From the cavity of the tym- the occipital bone ; it forms the upper and 



panum, where it is rather largest, it passes inner part; the tympanum the lower and outer, 



forwards and inwards, and near its termination The petrous bone is brittle and very thick. It 



appears very much fasciculated, as if glan- has a larger portion, an irregular ellipsoid, 



dular. (A probe passes through the Eusta- which gives attachment to the tympanum by 



chian tube in the figure, showing its nasal ter- its outer surface, and which contains the three 



mination at d.) semicircular canals ; and another smaller por- 



" The Eustachian tube and tympanum com- tion in the form of a quarter of a sphere, which 

 municate with several sinuses, which passing is separated from the first by a pretty deep de- 

 in various directions surround the bone of the pression, and is occupied internally by the 

 ear. Some of these are cellular, similar to the cochlea. The acoustic nerves enter by fora- 

 cells of the mastoid process in the human sub- mina at the bottom of the depression, 

 ject, although not bony. There is a portion of The tympanum is formed by a thick bony 

 this cellular structure of a particular kind, being plate folded longitudinally, so as to form a 

 white, ligamentous, and each part rather round- canal, open anteriorly, whence is continued the 

 ed than having flat sides.* Eustachian tube. It is closed behind, where 



" One of the sinuses passing out of the tympa- it assumes a bilobate figure, and adheres above 



num close to the membrana tympani, .goes a this part to the outer and posterior part of the 



little way in the same direction, and'commu- petrous bone by a rough process, which is 



nicates with a number of cells. firmly wedged in, but does not anchylose soon. 



" The whole function of the Eustachian It adheres to it also by a part of the external 



tube is perhaps not known ; but it is evidently margin, and it is between these two points of 



a duct from the cavity of the ear, or a passage adhesion that we find the very irregular opening 



for the mucus of these parts ; the external of the tympanum. The internal margin leaves 



opening having a particular form would incline a long interval between it and the petrous bone, 



us to believe, that something was conveyed to Beneath the bilobate portion of the tympanum 



the tympanum. the styloid process passes, which is attached 



" The bony part of the organ is very hard immediately behind it by ligaments to the de- 



and brittle, rendering it even difficult to be cut scending plate, which represents the mastoid 



with a saw, without its chipping into pieces, process. 



That part which contains the immediate organ The bone of the ear of the Cachalot displays 



is by much the hardest, and has a very small great relations with that of the Dolphins, 



portion of animal substance in it ; for when only the tympanum is shorter and less lobated 



steeped in an acid, what remains is very soft, behind. 



almost like a jelly, and laminated. The bone The bone of the ear in the Balanida differs 



is not only harder in its substance, but there is from that of the Delphinida by the enormous 



on the whole more solid bone than in the cor- thickness of the tympanum (a^jig. 276), espe- 



responding parts of quadrupeds, it being thick daily at the inner side. This tympanum is a 



and massy. little more closed anteriorly, but leaves between 



The part containing the tympanum is a it and the os petrosum (b) on the inner side a 



thin bone, coiled upon itself, attached by one proportionally shorter and wider interspace, 



end to the portion which contains the organ ; It is not bilobed posteriorly, 



and this attachment in some is by close contact The petrous bone is of a very irregular shape 



only, as in the Narwhale ; in others, the bones and knotty surface ; it gives off two large rough 



run into one another, as in the Bottle-nose and processes, of which one is situated behind and 



Piked Whales (liyperoodon and Balanop- a little above, and articulates with a corre- 



tera). spending process of the tympanum, is wedged 



" The concave side of the tympanum is between the temporal and lateral occipital 



turned towards the organ, its two edges being bones; and the other, situated anteriorly and 



close to it ; the outer is irregular, and in many below, is articulated by a squamous suture 



only in contact, as in the Porpoise : while in with the part of the temporal which descends 



others the union is by bony continuity, as in to furnish the articulation of the lower jaw. 



the Bottle-nose Whale ( Hyperoodon ), leaving This second process, which in the Bul<en<z is as 



a passage on which the membrana tympani is large as the other, is very small in the Bal<e- 



noptera ; nevertheless the ear-bone of the Ba- 



' These communications with the Eustachian i^ae i s fi xec l more solidly to the cranium than 



tube may be compared to a large bag on the bases ' c T\ i L- 



of the skull of the Horse and Ass, which is a lateral that ot the Uelptimi. 

 swell of the membranous part of the tube, and when 



distended will contain nearly a quart." * Oss. Foss. vol. v. pt. i. p 



2 Q 



